Ciao,

dai un'occhiata qui
http://stackoverflow.com/questions/5...on-time-in-php
http://www.webdesign.org/web-program...time.8722.html
http://www.developerfusion.com/code/...n-time-in-php/
http://derblub.com/get-accurate-scri...on-time-in-php

Devo pero' dire che basta fare una ricerca su Google...